That's because you can't chose where you 'tone'. You need a low body fat to see them, so your diet is key. There's nothing you should 'not' eat because it's all down to having a proper caloric deficit whilst hitting your daily macros for the required nutrients. It's also reasonable to assume, depending on your LBM, you might need to bulk then cut so you've actually got some mass in that area.
Personally my front squats hit my abs enough as it is, but I'll throw in a few sets of weighted leg raises (and hanging leg raises) if I have some extra energy spare after a workout.
I've started to swim 40 minutes every tuesday and thursday on my cardio days.
Would you say that will help? Or not any effect at all?
I've started trying to alter my workouts to focus on my abs, but I do find it hard.